This invention relates to a steerable drive axle for a motor vehicle.
A drive axle for a motor vehicle commonly includes a rigid tubular housing, a pair of dirigible wheels rotatably supported on the rigid tubular housing at opposite ends thereof, a pair of axle shafts in the rigid tubular housing connected to the dirigible wheels, and a differential in an expanded chamber in the middle of the tubular housing which distributes drive torque from a drive shaft to each of the axle shafts. Such drive axles are referred to as steerable when they further include steering knuckles between the ends of the rigid tubular housing and corresponding ones of the dirigible wheels, a pair of axle shafts with universal joints to transfer the torque while turning, and a steering apparatus which pivots to the steering knuckles in unison about respective ones of a pair of steering axes of the rigid tubular housing. A steering apparatus on a drive axle described in U.S. Pat. No. 4,592,440, for example, includes a steering assist fluid motor on a cover over the expanded chamber in the middle of the rigid tubular housing of the drive axle. The fluid motor includes a cylinder attached to or integral with the cover and a piston in the cylinder linked to the steering knuckles such that linear translation of the piston in the cylinder induced by differential fluid pressure across the piston effects corresponding pivotal movement in unison of the steering knuckles about the steering axes. A steerable drive axle according to this invention is a novel alternative to the steerable drive axle described in the aforesaid U.S. Pat. No. 4,592,440.
This invention is a new and improved steerable drive axle for a motor vehicle including a rigid tubular housing, a pair of steering knuckles at opposite ends of the rigid tubular housing pivotable about respective ones of a pair of steering axes of the latter, an expanded chamber in the middle of the rigid tubular housing open on one side for access to a differential gear set in the expanded chamber, a differential cover for closing the open side of the expanded chamber, and an electrically-powered steering apparatus integral with the cover linked to the steering knuckles. The electrically-powered steering apparatus includes a rack bar passage in the differential cover, a rack bar supported in the rack bar passage for linear translation in the length direction of the rack bar passage, a pinion head rotatably supported on the differential cover having a pinion gear meshing with a rack gear on the rack bar, an electric motor mounted on the differential cover, and a speed reducer on the differential cover between the pinion head and an output shaft of the electric motor. In a preferred embodiment, the speed reducer consists of a first planetary gear set having an input through a sun gear rotatable as a unit with the output shaft of the electric motor and an output through a planet carrier and a second planetary gear set having an input through a sun gear rotatable as a unit with the planet carrier of the first planetary gear set and an output through a planet carrier rotatable as a unit with the pinion head.